This booklet is intended to offer the beginner to 10 GHz operation a
general introduction to current practice in Ontario. It is not meant to
provide complete technical details on how to build equipment, but rather to
show what approaches are in common use and how the equipment is operated.

The 10 GHz band (10.0-10.5 GHz or 10000-10500 MHz) is one of the easiest
microwave bands to get on, primarily as a result of its proximity to
frequencies heavily used by various types of radars and the resulting
equipment availability.

The most popular mode of operation on the amateur 10 GHz band in Ontario at
present is wideband FM voice. By wideband, I mean the same bandwidth, more or
less, as used by commercial FM broadcast stations. Typically this means about
75 kHz deviation and a receiver IF bandwidth of about 200-300 kHz. In practice
this varies somewhat, depending on what equipment an individual amateur is
using, but this is about the centre of the range.

This is a departure from the usual amateur practice on lower frequencies,
where SSB and narrow band FM (about 5 kHz deviation) dominate for voice
communication. These modes can be used at 10 GHz, but wideband FM allows the
use of transmitters and receivers with relatively poor frequency stability.
This means that equipment can be bought or built at much lower cost than would
be needed for the more usual narrow band modes.

What do we give up by using wideband FM and simple equipment ? There are
basically two things: (1) the poor frequency stability of the equipment means
we can not just switch on the rig and be ready to communicate on a precisely
defined channel, as we do on 2m FM, for example, and (2) the signals for a
given power, antennas and distance, are not as strong as if we used a narrow
band mode. However, the range can be surprisingly good at very low power
levels.

Wide band FM activity in Ontario takes place mostly in the 10.200 - 10.400
GHz range.

Virtually all wideband FM equipment for 10 GHz can be described by the
block diagram of Figure 1. The transmitter consists of a tunable oscillator
(running directly on the transmit frequency) which is frequency modulated by
the audio signal from the microphone amplified in a modulator circuit. This
oscillator sends most of its output power to the antenna. A small portion of
the oscillator power is coupled to a mixer, which is also coupled to the
antenna. A 10 GHz signal received on the antenna arrives at the mixer and
beats with the transmit oscillator frequency to give an output at a lower
intermediate frequency (IF). The signal at the IF is then amplified,
filtered, detected and then fed to an audio amplifier and speaker or
headphones.

This is basically all there is to the transceiver. The differences
between various rigs are in the following areas:

-device used in the 10 GHz oscillator (Gunn diode or Klystron tube)

-modulator circuit used

-how the power is coupled between the oscillator, mixer and antenna

-design of the IF strip

-whether any extra gadgets (such as automatic frequency control or a tone
oscillator ) are used.

Wideband FM transceivers for 10 GHz have no transmit/receive relay or
other switching. They transmit and receive simultaneously and so a QSO using
one is much like talking on the telephone. If signals are strong you will
soon find yourself forgetting about things like saying "over"; it
is much more like a normal conversation than most amateur radio operation
is. To be able to do this, and with very simple equipment, there is one
peculiarity. That is, the transmit and receive frequencies for a transceiver
are not the same, and two transceivers in contact with each other must
transmit on different frequencies.

For example let's assume that station A has his oscillator tuned to
10.300 GHz (10,300 MHz). He is then able to transmit an FM signal at this
frequency. But the oscillator is also used as the local oscillator for the
receiver. If station A has an IF of 100 MHz, then he can receive stations on
10.3 GHz +/- 100 MHz. In other words, if the transmitter is tuned to 10.300
GHz, the receiver is automatically tuned to both 10.200 GHz and
10.400 GHz. Now if station B wants to make a contact with station A he can
tune his oscillator to 10.200 GHz. If he points his antenna at station A,
then (given a good path between them) he will be heard at station A. But if
he wants to hear station A transmitting on 10.300 GHz he must have his IF at
100 MHz; he will then receive on 10.100 and 10.300 GHz. This is one of the
odd things about 10 GHz wideband FM operation...both stations must have the
same intermediate frequency in order to work full duplex.

It is possible to make contacts when the stations involved have different
IFs but it is much more difficult. More on this in chapter 6.

The preferred IF in southern Ontario is 30 MHz. This is a North American
standard, resulting from the initial popularization of 10 GHz with the
Gunnplexer systems sold by Advanced Receiver Research. The second choice is
90 MHz (approximately), for those using FM broadcast receivers as IF strips.
In the UK, 10.7 MHz is commonly used, but it is rare here.

Waveguide

The transmission line of choice at 10 GHz is usually rectangular
waveguide. It has much lower loss than any kind of coaxial cable that is
suitable for this frequency. The most common size of waveguide for 10 GHz is
usually called WR90 (in North America). This stands for "Waveguide,
Rectangular, 0.90 inch". It is also known as WG16 in the U.K., IEC
R100, and by the U.S. military designations RG-52/U and RG-67/U. It is a
hollow metal tube with a rectangular cross-section of 0.90 by 0.40 inch
(inside) and 1.00 by 0.50 inch outside. It is intended to operate from
8.2-12.4 GHz. It is probably the most common waveguide to be found on the
surplus market because it has been used in many pieces of radar equipment
since the middle of the Second World War. Intruder alarm modules usually
have standard flanges for WR90 waveguide. The most common flange for
connecting two pieces of waveguide together is nearly square with four holes
for bolting the flanges together. The holes will either be tapped 8-32 or be
clearance holes for 8-32 screws.

Typical Rigs

Background

In this section I will describe several rigs which have been used in 10
GHz operations over the last few years. Some of these are completely
commercially built rigs, either intended for amateur operation or for
other purposes. Others are more or less home-brewed. They are:

- the Tellurometer: a South African distance measuring device for
surveyors, which tunes from 10.05 to 10.45 GHz and has a voice facility so
the surveyors could talk to each other. Many of these have been available
on the surplus market but beware, there are versions for other (non- ham)
frequencies too.

The Tellurometer uses a Klystron tube as the 10 GHz oscillator. I have
included it, although it is rather out of date, because of its
availability. Individual klystrons are also occasionally seen at flea
markets and in surplus electronics stores, but I have not described a home
brew rig based on one. This is because it is considerably more difficult
to build and adjust than a more modern solid state rig. I don't know of
anyone who has built a klystron rig in the last 20 years

The Tellurometer

There is a picture of Ralph, VE3BBM, operating one of these on the
front cover of the July/August 1989 issue of TCA. They were originally
intended as surveying instruments. With a pair of them, it is possible to
accurately measure the distance between two points using a link at 10 GHz.
More usefully to amateurs, however, the designers included a voice
communication capability and a telephone-like handset.

The 10 GHz oscillator is a klystron tube, mechanically tunable from
about 10.050 GHz to 10.450 GHz with a turns counter for relative frequency
readout. The klystron can be FM modulated by the audio from the handset
microphone. The deviation is larger than normal for amateur use, perhaps
about 150 kHz, but it can be copied on other rigs if the operator talks
softly. A small dish (around 10 inches in diameter) is built in to the
unit, and the power (a few tens of milliwatts) from the oscillator feeds
this dish through a short piece of waveguide with 45 degree slanted
polarization. A mixer diode mounted near the dish focus is set up to
receive signals with the opposite slant polarization. Because the
oscillator and mixer are cross-polarized, only a little of the oscillator
power is coupled to the mixer diode. This method of coupling the power
from the oscillator to the antenna and from the antenna to the mixer
without putting too much transmit power into the mixer is often referred
to as a "polaplexer". The mixer feeds an IF amplifier and FM
detector operating somewhat above 30 MHz. The detected output is amplified
(not quite enough, according to some owners!) and provided to the earpiece
in the handset. There is an automatic frequency control circuit to lock
the klystron to follow the frequency drift of the incoming received
signal.

The power needed for the rig is obtained from a 12 V source. However,
an internal inverter is used to obtain the high voltages needed to run the
klystron. Everything else is solid state. It takes quite a lot of current
from the supply (more than 1 amp, I believe).

If you find a Tellurometer at a flea market or surplus store, be sure
to determine if it is the 10 GHz kind, or for some other frequency band.
The 10 GHz version that I am most familiar with has about a 10 inch dish
with a feed which is made (at least partly) of WR-90 waveguide.

The TR10GA

This is the only commercially manufactured 10 GHz amateur wideband FM
transceiver that I am aware of. It consists of a MA/Com Gunnplexer
microwave unit and an IF/modulator board packaged in an attractive case
with all the controls and connectors needed in a complete rig. A small
horn antenna is normally supplied with the transceiver. It is sold by
Advanced Receiver Research (ARR) of Burlington, Connecticut. A block
diagram of the TR10GA is given in Figure 2.

The Gunnplexer consists of a varactor-tuned Gunn diode oscillator, a
mixer diode and a circulator in a small assembly (a bit smaller than a 2
inch cube). A circulator is an extremely clever gadget. It has three
connectors (or equivalent, such as waveguide). The antenna is connected to
one, the oscillator to another, and the mixer to the third. The effect of
the circulator is to cause nearly all the oscillator power to be directed
to the antenna and only a little to the mixer; at the same time nearly all
the power received on the antenna from a distant station is directed to
the mixer, and only a small amount goes to the oscillator and is lost. The
Gunn diode oscillator runs from a regulated 9 volts, and is tuned by
varying the voltage on a varactor (variable capacitance) diode mounted in
the oscillator's resonant cavity. A 10 GHz Gunnplexer can be tuned this
way over at least 60 MHz and often as much as 100 MHz. The oscillator is
frequency modulated by superimposing a small audio signal from the
microphone on the varactor tuning voltage. ARR supplies Gunnplexers with
the centre of the tuning range at either 10.250 or 10.280 GHz.

The IF/modulator board contains the circuitry needed to provide the
tuning and modulation voltage to the varactor, the 9V regulator for the
Gunn diode and a 30 MHz IF strip. The IF receiver is a superheterodyne,
with a crystal controlled converter down to a 10.7 MHz IF, where the
signal is amplified and detected in a CA3189E IC, originally designed for
FM broadcast radios. An audio amplifier provides plenty of sound through
headphones or speaker. Two meters display the varactor tuning voltage (or
discriminator output voltage) and the signal strength. There is also a
squelch function and automatic frequency control to lock the Gunn
oscillator to follow the frequency of the incoming signal.

Both the Gunnplexer and the IF/modulator board (model RXMR30VD) are
available separately from ARR for those who want to do their own
packaging.

Figure 2: Simplified Block Diagram of TR10GA Transceiver

A SOLFAN Rig

Perhaps the most common type of (more-or-less) home brew transceiver is
based on the microwave unit from an intruder alarm made in large numbers
by SOLFAN. These were in wide use all over North America until recently.
They have been removed from use in large numbers during the 1980's and
have been quite available from surplus outlets and sometimes from alarm
companies, usually for $5 - $30. The most useful type has a cast body
including a Gunn diode oscillator (without varactor tuning) and a mixer
diode in the waveguide between the Gunn oscillator and the output flange.
Similar microwave units are made by other manufacturers. Probably the most
common on the surplus market are made by Alpha.

The Gunn oscillator will run from a voltage of about 6 - 9V (positive
with respect to the case), at about 100 mA. Normally, the power supply for
the Gunn is set up to have the voltage variable over about this range
which has the effect of varying the frequency of oscillation by up to 40
MHz or so. The audio signal from the microphone is amplified and added to
the power supply voltage to provide FM modulation. These
power/tuning/modulation functions can be done with a simple circuit of as
little as two ICs, which is all that is really needed in addition to the
SOLFAN microwave unit to make a functional transmitter. See Figure 3 for a
block diagram. Often, a tone oscillator is also provided, which can
provide an alternative audio modulation signal (instead of the microphone)
for tuning or for Morse operation when signals are weak. The output of the
intruder alarm units is usually about 5 - 10 mW at 10 GHz. In alarm
operation they are normally tuned to about 10.525 GHz and must be retuned
into the amateur band before they can be used for communication. This is
usually easily done, providing a frequency measuring instrument is
available (see section 4.3).

On the receive side, the mixer diode terminal is connected (usually
through a piece of coaxial cable) to a low noise preamplifier. This feeds
an IF receiver. Some of the options for this receiver include:

-an FM broadcast radio, usually tuned to about 90 MHz. Car radios are
good, but the modern synthesized type can be more difficult to use than
the older ones with continuous tuning.

-a modified FM broadcast radio, with the front end rebuilt to receive
30 MHz, the preferred IF. I have one rig with two selectable circuit
boards from FM stereo receivers, one "as is" and one converted
to 30 MHz. The stereo decoder and audio sections were literally sawn off
and a simpler audio amplifier substituted.

-a homebrew receiver based on the Philips TDA7000 "FM radio on a
chip" IC, which can be used at either 30 or 90 MHz. An LM386 IC makes
a good audio power amplifier.

-a somewhat more complicated homebrew superheterodyne receiver with 30
MHz input and a 10.7 MHz second IF, usually employing a single chip
IF/detector IC such as a CA3089E, CA3189E, ULN2111, etc.

Normal practice is that 30 MHz IF strips are fixed-tuned, but 90 MHz
IFs are tunable to allow the operators to select a frequency not subject
to break-through interference from local FM broadcast stations.

Keep in mind that the standard is wideband FM, so an unmodified
10m FM transceiver or narrow band FM scanner is not suitable for the IF
receiver.

Separate Gunn diode oscillators are also frequently available as
surplus, including alarm units from SOLFAN and others, and higher power
oscillators from police speed radars can sometimes be found. The best way
to use these to build a transceiver is to acquire a circulator and a
waveguide detector/mixer unit (see also section 4.2). When connected as
shown in Figure 4 the bulk of the oscillator signal will go to the antenna
and the most of the power of any signal received by the antenna will be
directed to the detector (in this case used as a mixer). Since these
various pieces are not usually designed to operate together, a good check
is to measure the current from the mixer diode terminal to the case; it
should be somewhere in the range of 0.2 - 2 mA, for best operation. The
modulator and IF circuits can be the same as described in the previous
section.

If you manage to acquire a higher power Gunn oscillator, say in the
100-200 mW output range, there are some additional points to consider.
Usually the supply voltage for such devices is a little higher, often
10-12 V, so you may not be able to use a 12V battery to run a simple
variable supply tuning/modulator unit as some voltage drop will be needed
to make it work. Also, never short the waveguide output from the
circulator (the antenna connection). If you do, all the oscillator power
will be reflected back into the circulator and, since it is apparently
coming from the antenna, will be directed to the mixer. This power level
can be enough to burn out the mixer diode.

Figure 4: Transceiver Using Separate Gunn Oscillator and
Mixer

Antennas

Horns

Horn antennas are simply tapered waveguide sections. If the length of
the taper is sufficient for the size of the horn aperture, the energy
will be nearly in phase over the aperture, which results in higher gain
than from a piece of open WR-90 waveguide. Such an antenna also has the
advantage of being very broadband and having low VSWR, so long as the
taper is sufficiently long and the walls are smooth (no sharp steps).

The gain available runs from about 6dBi (for open waveguide) to about
24 dBi. Horns can be made with larger gains but the required length of
the taper begins to increase extremely quickly and soon becomes
impractical. Often, SOLFAN and other alarm equipment is obtained with
small horn antennas attached. These are great for initial testing but
are generally not adequate for long distance work. Advanced Receiver
Research sells 17 dBi gain horns which are typically good for some tens
of kilometres (more if the station on the other end has a bigger
antenna). It is not too hard to make horns out of double-sided PC board
material or sheets of hobby brass or galvanized iron. Some of the
articles in the bibliography describe how to make them. Many people find
the layout of a pattern for cutting the horn parts to be the hardest
part; a knowledge of trigonometry is useful, although trial-and-error
also works.

Reflectors

The "standard" antenna for 10 GHz wideband FM stations all
over North America seems to be a parabolic reflector ("dish")
about 2 feet in diameter. Most have been obtained from surplus sources
although occasionally US suppliers of new dishes with reasonable prices
can be found. Dishes have (usually) higher gains than horns, ranging
from about 20 dBi for a 6 inch diameter reflector to about 40 dBi for a
5 foot diameter dish. Dishes smaller than 6 inches are too small to work
well and anything larger than 5 feet has such a small beamwidth that it
is very difficult to aim; so this is about the range of sizes that is
actually used. The beginner is advised not to start out with a dish much
more than 2 feet across until some experience in aiming the antenna is
gained. Most reflector antennas in use by amateurs are of the symmetric
type, although a few have tried offset reflectors such as those used for
Direct Broadcast Satellite TV reception.

Antenna Supports

Most 10 GHz FM operation is by portable stations who normally use some
sort of tripod to support the antenna and at least some part of the
electronic part of their equipment. Most common are camera tripods, with the
screw removed or with an adapter to fit it built into the antenna. Very
inexpensive
camera tripods are adequate for horn antennas but for a 2 foot dish, a
medium to heavy duty tripod is required. It is useful to have a pan/tilt
head to allow the antenna to be steered in both azimuth and elevation.
However, if necessary, the elevation control can be had by adjusting or
moving the tripod legs. Surveyors' tripods are also excellent, being heavy
duty and tall (good for getting the signal over walls, fences, hedges,
etc.). They normally need some sort of modification to mount antennas,
rather than the standard mount for theodolites, etc. A simple homebrew
tripod can be made quite cheaply, by connecting three 4 foot long legs (1
inch dowels or 1x2 inch lumber) to a top plate a few inches across using
hinges. A bolt through the top plate provides a pivot for azimuth rotation.
One practical word of caution regarding dishes and tripods: they blow over
easily in a wind. On a windy day you will need to find a way of guying the
tripod or you must stand beside it at all times to prevent it from toppling.

Other support methods can be used. For small rigs with horn antennas the
top of a car, or the tailgate of a truck or hatchback, or a small folding
table, can be used. I have even seen VE3MNA making contacts with a 2 foot
dish held under his arm. It worked well but is not recommended to the
beginner !

If you live on a hill and want to try 10 GHz from home, with a
tower-mounted antenna, there are a couple of things to keep in mind. With a
horn antenna, any normal rotator will work well. However, with a dish of 2
feet or so, it will become somewhat difficult to aim using a HAM-M type
rotor, due to the narrow beamwidth. Also, the force due to wind on the dish
can be considerable, so ensure that the structure is adequately strong.

The first nearly indispensable piece of test equipment I will mention is
a signal source for testing your receiver. The easiest to find is a Gunn
oscillator, which can be found from time to time at surplus stores or at
flea markets and hamfests, usually for $5 - $10. You may also be able to
convince an alarm company to give or sell you one or more from the units
they have taken out of service. For the purpose of generating a signal to
listen to, you don't need the mixer diode, so a Gunn-only type will be
entirely satisfactory. You will probably want to equip it with a modulator
of the type used in a transceiver so that you can produce a modulated FM
signal to listen to on your main transceiver. Of course, once you start down
this road you will probably end up with another complete transceiver before
long, which is an even better piece of test equipment.

Surplus commercial signal generators that cover the 10 GHz band are also
to be found occasionally, though they will cost you much more than a Gunn
oscillator.

Detector

A waveguide mounted RF detector is extremely useful to have. The obvious
purpose is to find out if there is any output from your transmitter (or test
source). It can also be used with an absorption wavemeter to measure your
transmit frequency or as a "Boomerang" (see 4.4). There are 3 main
options here.

1.You can use the mixer diode in a Gunn/mixer alarm unit as a detector.
Just connect a microammeter to the terminal and to the waveguide body to get
a readout. Be careful of static electricity...it can burn out the mixer
diode in an instant.

2. Use a surplus WR-90 waveguide detector mount. Usually these have 1N23
type or similar diodes in them which are easily replaced if you zap them (if
you can find a supply of diodes!). Use it the same way as #1. These usually
have a BNC connector for the output voltage. Surplus price is often about
$10. Sensitivity of surplus detectors varies considerably, due to the use of
different detector diodes and because the devices may not be tuned for best
response in the amateur band.

3. Use a waveguide to coaxial transition and a coaxial detector. Coaxial
detectors that work up to 10 GHz are not that common (because they are often
still useful to industry and government) but they do show at hamfests and in
surplus stores occasionally. The waveguide to coax transition will normally
have either an N-type or SMA fitting, never BNC. Use it the same way as #1.

Absorption Wavemeter

This is a very useful gadget. It is essential if you are going to use
surplus Gunn oscillators that you have (or have access to) a frequency
measuring instrument. If you know someone with a frequency counter that
works at 10 GHz, use it. However, most of us are stuck with the older
technology of absorption wavemeters. The wavemeter consists of a piece of
waveguide (or coaxial cable) with flanges or connectors on both ends,
coupled lightly to a precisely tunable resonant cavity. You put microwave
power in one end and a detector at the other end. As you tune the cavity
through the frequency of the microwave signal, you will notice a drop in the
power detected, as some of the power is sucked into the cavity and absorbed
in its walls.

These units are available from time to time in the usual surplus channels
(flea markets, surplus electronics outlets). The best are the Hewlett
Packard X532A or X532B models which have WR-90 waveguide interfaces and
cover 8.2-12.4 GHz with an accuracy of +/-8 MHz or better. These typically
sell as surplus for $50 - $100. There are other manufacturers, as well. It
is also possible to modify and recalibrate the wavemeters from the military
TS-147 radar test set which normally tune a range just below the ham band. I
found one (just the wavemeter) in a surplus store for $25 a few years ago.

Boomerang

The so-called boomerang consists of a waveguide detector, perhaps with a
small horn antenna connected to the waveguide flange, and with a low power (up
to a few milliwatts) signal generator tuned to your transceiver's IF connected
to the normal detector output connector. It is used to check both the
transmitting and receiving capabilities of a wideband FM transceiver, as
follows. Set the device up a few feet from, and pointing at, the transceiver'
antenna. Switch on the transceiver and the signal generator attached to the
detector. The transceiver will emit a signal at frequency f

TX
which is then received by the boomerang. In
the waveguide detector diode it will mix with the signal generator frequency fIF
to produce two new signals at fTX +/-
fIF.
These signals are then radiated back toward your rig and, since they differ
from the transmit frequency by the IF, they can be received. This allows you
to monitor the sound of your transmitted modulation.

SHF Parts in Indiana usually has a selection of Gunn oscillators and
intruder alarm microwave heads. A few parts useful for WBFM can be obtained
from Down East Microwave Inc. in New Jersey. Other suppliers exist; they
tend often to be "one-man shows" or part-time basement businesses
which can come and go in a short time or have limited stocks.

Alarm Companies

Alarm companies are a variable lot. Microwave intruder alarm units are no
longer held in very high regard as they are apparently prone to quite high
rates of false alarms. What the companies do with units that are taken out
of service ranges from throwing them out to actually giving them to radio
amateurs. It depends on the individuals at the local offices, it seems. It
is certainly worth giving them a call to see if they would be willing to
sell or give you old units. Tell them the whole story of what you want to do
with them so their fears that they may be giving equipment to start-up
competitors will be reduced. Certainly several Ontario amateurs have been
able to acquire numbers of units at very reasonable cost.

Hamfests

Try your local amateur radio flea markets. You never know what you might
find. If you want to venture further afield, the annual hamfests in Dayton,
Ohio and Rochester, New York (both in May) are probably the among the best
places to find microwave parts.

Most 10 GHz wideband FM operating is done with portable equipment at
locations away from home. This is because good high locations are needed to
be able to make contacts over long distances with this simple equipment.

Selecting
Operating Sites

A good operating site is usually one with a spectacular view. Paths that
can normally be worked are only slightly longer than one can see from the
operating site. Just as they do for your view of the scenery, buildings,
trees, and so on block the signal. Except for the shortest of paths, the
takeoff in the direction of the other station must be clear of such
obstacles.

Pointing the Antenna

6.3.1 When the Other End is Visible

If the operator at the other end of the path is located at a clearly
visible landmark such as a ski hill or a tall building then you merely need
to aim your antenna by eye at the landmark. A pair of binoculars or small
telescope can be very useful in identifying less obvious objects, such as
individual houses or communications towers. Don't forget that if you are
using a dish of a foot or more in diameter, it will likely be necessary to
aim in both azimuth and elevation to get the best signal.

When the Other End is Not Visible

If the weather is not clear, there are no landmarks to sight on, or the
path is beyond the horizon then other approaches are needed. A magnetic
compass will be found to be nearly indispensable. A toy compass will not
normally offer the necessary accuracy; a sighting compass of some sort will
be needed. A number of types are available, the most common being the type
sold for orienteering and the "lensatic" compass, both of which
are quite satisfactory. Reasonably accurate bearing information can be
obtained using a protractor and a ruler on a map (preferably a topographic
map). Don't forget to add the amount of the magnetic declination to the True
bearing obtained from the map to get the magnetic bearing you will aim the
antenna along. For example, from the map you may determine that the other
station is located to your north-east (True Bearing of 45 degrees). The
magnetic declination in your area may be 10 degrees (typical of much of
southern Ontario in the 1990s), so the bearing you will need to read from
the compass is 55 degrees.

A good map may also yield other approaches to finding the path bearing.
One way that is quite often useful is to find a bearing with respect to a
road you are on. If the path is just a few degrees off the direction of the
road, or nearly perpendicular to the road, you can likely get the antenna
pointing quite close without a compass or other instrument. The author has
also used an easily constructed version of the "cross-staff", a
medieval navigational instrument, to find bearings with respect to nearby or
clearly visible landmarks.

Talkback

It is rare to be able to make a contact on 10 GHz either randomly or
without some real-time coordination between the operators involved in a
scheduled contact. Usually, the operators will coordinate their frequency
settings, antenna bearings, etc. on 2m FM. The frequencies most often used
in southern Ontario and western New York are 146.55 and 146.58 MHz simplex.
However, if the 2m equipment is not sufficient for direct contact, any
available repeater may be pressed into service. Because of the unusual
nature of the communications, it can be difficult to use a repeater for
talkback if there is any other activity on the frequency, so simplex is
preferred.

Surprisingly, it is not uncommon for the 2m simplex path to be difficult
or impossible to work with mobile or handheld rigs running a few watts, but
when everything is finally set up on 10 GHz, the microwave signals (with
only a few milliwatts) are excellent, full quieting quality ! For this
reason it is advisable to have available a small 2m beam if paths much more
than 50 km are to be tried.

Especially if there is 10 GHz narrow band (SSB,CW) activity under way,
there may be talkback activity on 2m SSB. 144.200, 144.260 and 144.300 have
been used in recent years.

Propagation

There are two fundamental propagation modes that are useful for 10 GHz
wideband FM. These are line-of-sight and tropospheric ducting. In fact, when
the term line-of-sight is used for microwave propagation it usually implies
that the small average amount of tropospheric ducting that is normally
present is factored into the expectations of whether a path can be worked or
not. Thus, a microwave line-of-sight path, during average conditions, can be
slightly further than can actually be seen, say with a telescope. The
beginner, however, will do well by starting off with truly optical
line-of-sight paths as they will tend to be less variable from day to day.
While paths slightly over the optical horizon will often work well, local
obstructions near either end of the path can eliminate any chance of a
contact. A building, or even a single tree in the direction of the other
station and within a few hundred metres of one end of the path, is usually
enough to drop the signal below the detection threshold. Short paths which
are blocked in this way can occasionally be worked by a reflection path,
where both stations aim their antennas at a large object visible at both
ends. In southern Ontario, the longest paths workable by line-of-sight
propagation are a little more than 100 km in length. If only we had some
real mountains!

Under typical conditions, stations with 2 foot dishes and 10 milliwatts
can work each other over any line-of-sight path in southern Ontario. With
horn antennas some of the longer paths may be more difficult.

Tropospheric ducting is the propagation mode responsible for distant UHF
TV reception and the "lifts" often experienced on 2m, mostly in
the summer and fall. To be useful for 10 GHz, the ducts must form at ground
level (so the antennas will be in the duct). Reception of distant UHF TV
stations at much better than normal signal strengths appears to be a good
indicator of these ducts. It tends to be difficult to make good use of them
for 10 GHz wideband FM because they usually happen at night and early in the
morning, at which time you need to arrange with another ham to go to
portable sites, probably more than 100 km apart to try for a contact. A 10
GHz-equipped home station at a good location may have a better opportunity.
Contests offer a chance to be out there anyway, and if interesting
propagation happens you will be ready. It is worth keeping in mind that a
number of contacts of more than 1000 km in length have been made around the
world using wideband FM and tropospheric ducting propagation.

It has been the experience of the active 10 GHz amateurs in southern
Ontario that paths over the Great Lakes can be enhanced substantially at
times, and conversely, over-water paths that are clearly line-of-sight can
on occasion be unworkable with 10 GHz WBFM equipment.

Making the Contact

6.6.1 Choosing Frequencies

In Ontario, the usual practice is to use nominal transmitting frequencies
selected from a set of "channels" spaced 30 MHz apart. This
practice is derived from the availability from Advanced Receiver Research of
Gunnplexers with their nominal frequencies factory preset to 10.250 and
10.280 GHz. To maintain compatibility with these Gunnplexers, amateurs using
other equipment usually set their Gunn oscillators to these frequencies or
other frequencies separated from them by multiples of 30 MHz. The
frequencies in common use are 10.220, 10.250, 10.280, 10.310, 10.340, 10.370
and 10.400 GHz. Stations using 90 MHz IFs will usually select frequencies
from this list as well. There is no particular reason to pick a given
frequency...just agree with the station you want to work on what frequencies
to use. Sometimes, surplus Gunn oscillators designed for 10.525 GHz will not
readily tune below 10.3 GHz or so, so in this case the higher frequencies
must be used.

Finding the Signal

It is normally necessary to tune around a bit to find the other
station's signal. As well, particularly if a dish antenna (rather than a
horn) is used, the antenna must be rocked back and forth as well. The
combination of tuning and antenna-turning can sometimes take several
minutes to succeed, even if when everything is eventually peaked, the
signals are full-quieting. For beginners it is probably best that only one
of the two stations tune and turn the antenna at a time, while the other
sets the Gunn frequency to the frequency agreed on (as accurately as he
can). If this doesn't work, then you can trade roles and try again.

6.6.3 Tone Modulation

The capability of modulating the transmitter with an audio tone rather
than voice can be very helpful when trying to establish contact. A
continuous tone stands out from the background noise much better than
intermittent speech. As well, if the tone can be keyed, a Morse contact
can sometimes be successfully completed when the received signal is too
weak to copy voice.

Dealing with Frequency Drift

Simple Gunn oscillators are not overly stable in frequency as they warm
up and with respect to variations in the temperature of the environment.
Temperature changes (of the Gunn oscillator housing) due to the Sun being
obscured by clouds or due to gusts of wind can be noticeable. M/ACOM
Gunnplexers are rated for <250 kHz drift per degree (Celsius) of
temperature change. The lower quality SOLFANs are probably worse. It is
normally necessary to keep a hand on the Gunn tuning knob to keep the
other station tuned in properly. A few amateurs in this area have
automatic frequency control; that is, once a signal is received, their
Gunn will be automatically locked to follow the drift of the received
signal.

What if the IF's Don't Match ?

If the two stations trying to work each other have different receiver
intermediate frequencies, then they will not be able to work in full-duplex
mode. However, they can still work each other, if at least one of them has
enough Gunn tuning range so that the frequency difference between their two
oscillators can be set to be equal to either of the IFs. Then, when one
station is transmitting, the Gunn is set so the frequency difference is
equal to the IF of the receiving station. Then when the other station wants
to transmit, one of the Gunns must be tuned so that the frequency difference
between them is equal to the IF of the new receiving station. It is
inconvenient and usually takes considerable setting up through the talkback
rig, but it does work and can be quite smooth in operation with two
operators who are accustomed to it.

Contests

There are seven North American contests annually in which contacts on 10
GHz are eligible for points. They are the best times to expect significant
amounts of 10 GHz activity, but are not the best time to test a new rig, as
the more serious competitors will be in a hurry and not too keen to help out
in a long set of experimental adjustments.

The seven contests are:

-January ARRL VHF Sweepstakes: all bands from 50 MHz and up are eligible
and contacts on the microwave bands are worth more points than on the lower
frequencies. It's usually awfully cold for portable operation, so 10 GHz
activity is rare. The contest exchange and multiplies are 4-character grid
square so no complicated geographical calculations are needed.

-June ARRL VHF QSO Party: all bands from 50 MHz and up are eligible.
Scoring is different from January but is still based on 4-character grid
squares and awards extra points for microwave contacts. Stations in the Rover
category frequently take 10 GHz gear along.

-June ARRL Field Day: all amateur bands are eligible. There are no extra
points for microwave contacts. 10 GHz counts exactly the same as 40m. But it
is a good excuse to show off something different to your local club members.
There is usually no concentrated activity...you will have to set up contacts
with a friend or two.

-July CQ World-Wide VHF Contest: all bands from 50 MHz and up are eligible.
Scoring is based on 4-character grid squares and extra points are given for
microwave contacts. There is very little activity in this contest in the Great
Lakes region for some reason.

-August ARRL UHF Contest: all bands from 220 MHz and up are eligible.
Scoring and exchange are similar to the June contest but with more points
being given per contact. Without six and two metres, this one is a bit more
relaxed and you have a better chance of obtaining the patient cooperation of
other operators that is often needed for 10 GHz contacts.

-August/September ARRL 10 GHz and Up Contest: 10 GHz is the lowest and most
popular frequency eligible for points in this unusual contest. It takes place
over two weekends about a month apart from 8AM to 8PM local time Saturday and
Sunday (expect a change of hours in 1999). This is really the big event of the
year for many 10 GHz operators. Rules are very unusual, allowing repeat
contacts over and over with the same station if each contact is a
substantially different path. Exchange is the full 6-character grid square and
score is based on distance worked, so you need to know where you are !

-September ARRL VHF QSO Party: Same rules as June.

For contest rules and results see QST magazine or www.arrl.org for the ARRL
contests and Field Day and CQ magazine for the July contest.

Activity tends to be centred around a few areas with several particularly
active amateurs. Over the past few years the region in Ontario with the
highest concentration of activity have been in the southwest
(London/Kitchener/Cambridge/Georgetown). However, other areas have also been
represented, by operators based in and North of Metropolitan Toronto, the
Ottawa area, Chatham, Stoney Creek, Burlington and Oakville, for example. For
paths across the Great Lakes, there has been activity based in the Rochester,
New York area and in the extreme westerly part of New York state. There is
also an active group in the Montreal area.

The following list of amateurs in Ontario includes most of those known by
me to have been active on 10 GHz WBFM in the last few years, either with their
own, or borrowed, equipment:

A list of operating sites in and around Southern Ontario is provided on the
following pages. Most of these sites have actually been used for 10 GHz or
other microwave contacts. There are doubtless many more good sites that have
not been identified yet.

To determine if a given path between two locations is likely to work on 10
GHz wideband FM it is useful to plot the path that the signal will take with
respect to the hills and valleys between the two sites. If the signal must
pass through a large hill, then the path is unlikely to be workable. There are
three approaches:

(1) take measurements of distance and height of the intervening land from a
topographical map and plot on special graph paper which accounts for the
curvature of the Earth and the typical tropospheric refraction effects.
Samples of these graphs are given in the book by Saveskie. See section 11.7.

(2) plot the same data on ordinary graph paper, but after applying some
simple formulas to transform the Earth into a flat surface and the
line-of-sight into a curve ! This is actually quite easy and is described in
the articles by N7DH listed in 11.7.

(3) use a computer program. Several are available but I have no references
for them. I made up an EXCEL spreadsheet for my own use to perform
calculations by N7DH's approach.

The "Maidenhead Locator" system is a worldwide system of
coordinates that allows a location on the Earth to be defined in a few
characters, somewhat more briefly than using latitude and longitude numbers.
It is used as an exchange in most VHF (and up) contests. It is a bit complex
to explain here; the references in Section 11.8 should be consulted. The ARRL
and other organizations publish maps showing the "4-character grids"
which are the intermediate level of accuracy in this system. The 10 GHz-and-up
contest uses the more accurate 6-character sub-squares; you will need to
consult a topographic map or a Global Positioning System receiver to determine
your location accurately enough to know which of these sub-squares you are in.
The six character locators for some operating sites are given in the table on
the following pages

This list contains any references related to 10 GHz wideband operation
that I am aware of. It is by no means complete. This section is sorted into
several categories according to the main subject of the article. Within each
section the articles are in no particular order. There are many more
articles that pertain to narrow band operation on 10 GHz which are not
listed here. I have not attempted to put together any information on World
Wide Web sites dealing with amateur 10 GHz operation, but there are a number
of interesting ones, often dealing with operating and operators, rather than
technical details.